1. Field of the Invention
The present invention concerns a combustion chamber for a gas turbine in accordance with the preamble to claim 1.
2. Discussion of Background
Because of the extremely low NO.sub.x, CO and UHC emissions specified for the operation of a gas turbine, many manufacturers are starting to use premix burners. One of the disadvantages of premix burners is that they go out at very low excess air numbers, at a .lambda. of about 2, depending on the temperature downstream of the compressor of the gas turbine group. On the other hand, the "lean premix combustion" leads to poor combustion efficiency in the lower load range of a combustion chamber and to correspondingly high NO.sub.x, CO and UHC emissions. Particularly in the case of multi-shaft machines, this problem becomes critical because the combustion chamber pressure at idle is then typically very low. For this reason, the air temperature after the compressor is also low. In the case of oil combustion, the situation then becomes particularly difficult where the air temperature is less than the boiling temperatures of a major proportion of the fuel fractions. A suggested way of dealing with this problem consists in supporting the premix burner by one or several pilot burners in the part-load range. Diffusion burners are usually employed for this purpose. Although this technique permits very low NO.sub.x emissions in the full-load range, this supporting burner system leads to substantially higher NO.sub.x emissions during part-load operation. The variously reported attempts to operate the supporting diffusion burners with a leaner mixture or to use smaller supporting burners must fail because the burn-out becomes worse and the CO and UHC emissions are increased greatly. Among specialists, this condition has become known as the CO/UHC-NO.sub.x dilemma.